could 2009 be a scary year for particle physics?vjm/lectures/particlephysics2009_files/30th... ·...

22/10/2009 12:45BBC NEWS | Science & Environment | 'Big Bang' experiment starts well

of 4http://news.bbc.co.uk/1/hi/sci/tech/7604293.stm

BBC NEWS CHANNEL

Guide Science Engineering Computing Q&A Analysis

'Big Bang' experiment starts well

The LHC has been in construction forsome 13 years

We will be looking at whatthe Universe was made ofbillionths of a second after theBig Bang

Dr Tara Shears, University ofLiverpool

What is the Large Hadron Collider?

By Paul Rincon Science reporter, BBC News

Scientists have hailed asuccessful switch-on for anenormous experiment whichwill recreate the conditions afew moments after the BigBang.

They have now fired two beamsof particles called protons aroundthe 27km-long tunnel whichhouses the Large Hadron Collider(LHC).

The £5bn machine on the Swiss-French border is designed to smashprotons together with cataclysmic force.

Scientists hope it will shed light on fundamental questions in physics.

The first - clockwise - beam completed its first circuit of theunderground tunnel at just before 0930 BST. The second - anti-clockwise - beam successfully circled the ring after 1400 BST.

So far, all the beams have beenstopped, or "dumped", after just afew circuits.On Thursday, engineers hoped toinject clockwise and anti-clockwiseprotons again, but this time theyplan to "close the orbit", lettingthe beams run continuously for afew seconds each.

The BBC understands that low-energy collisions could happen in thenext few days. This will allow engineers to calibrate instruments, butwill not produce data of scientific interest.

"There it is," project leader Lyn Evans said when the beamcompleted its lap. There were cheers in the control room whenengineers heard of the successful test.

Montage of key moments from switch-on

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Page last updated at 11:23 GMT, Wednesday, 10 September 2008 12:23 UK

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SEE ALSOGod particle discovery 'likely' 10 Sep 08 | Edinburgh, East and Fife

Large Hadron Collider: Guide introduction 03 Sep 08 | Science & Environment

Cern lab set for beam milestone 07 Aug 08 | Science & Environment

Cern lab goes 'colder than space' 18 Jul 08 | Science & Environment

Earth 'not at risk' from collider 23 Jun 08 | Science & Environment

Cern particle lab schedule slips 25 Jun 07 | Science & Environment

Failure during Cern magnet test 03 Apr 07 | Science & Environment

Energising the quest for 'big theory' 03 Jan 06 | Science & Environment

Underground search for 'God particle' 04 Feb 05 | Science & Environment

RELATED BBC LINKSBig Bang Machine

RELATED INTERNET LINKSLHC (Cern)

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22/10/2009 12:44BBC NEWS | Science/Nature | Hadron Collider halted for months

Page 1 of 2http://news.bbc.co.uk/1/hi/sci/tech/7626944.stm

BBC NEWS CHANNEL

The LHC has been in construction forsome 13 years

What happened in the machine?

Superconducting magnets are cooled down using liquid helium

The Large Hadron Collider near Geneva will be out of action forat least two months, the European Organization for NuclearResearch (Cern) says.

Part of the giant physics experiment was turned off for the weekendwhile engineers probed a magnet failure.

But a Cern spokesman said damage to the £3.6bn ($6.6bn) particleaccelerator was worse than anticipated.

The LHC is built to smash protons together at huge speeds,recreating conditions moments after the Big Bang.

Scientists hope it will shed light on fundamental questions in physics.

Section damaged

On Friday, a failure, known as a quench, caused around 100 of theLHC's super-cooled magnets to heat up by as much as 100 degrees.

The fire brigade were called out after a tonne of liquid helium leakedinto the tunnel at Cern, near Geneva.

Cern spokesman James Gillies saidon Saturday that the sector thatwas damaged would have to bewarmed up from its operatingtemperature - of near absolutezero - so that repairs could bemade, and then cooled downagain.

While he said there was never anydanger to the public, Mr Gilliesadmitted that the breakdownwould be costly.

He said: "A full investigation is still under way but the most likelycause seems to be a faulty electrical connection between two of themagnets which probably melted, leading to a mechanical failure.

"We're investigating and we can't really say more than that now.

"But we do know that we will have to warm the machine up, makethe repair, cool it down, and that's what brings you to two months ofdowntime for the LHC."













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Page last updated at 11:55 GMT, Saturday, 20 September 2008 12:55 UK


Hadron Collider halted for months

SEE ALSOLarge Hadron Collider: Guide introduction 03 Sep 08 | Science/Nature

Earth 'not at risk' from collider 23 Jun 08 | Science/Nature

Cern lab goes 'colder than space' 18 Jul 08 | Science/Nature

Failure during Cern magnet test 03 Apr 07 | Science/Nature







| News feeds



2008 was a very exciting year for particle physics...

The £5bn Large Hadron Collider (LHC) is intended to smash protons - one of thebuilding blocks of matter - into each other

Repairing the Large Hadron Collider (LHC) near Geneva willcost almost £14m ($21m) and "realistically" take until at leastnext summer to start back up.

An electrical failure shut the £3.6bn ($6.6bn) machine down in


Page last updated at 18:17 GMT, Monday, 17 November 2008


Hadron Collider repairs cost £14m

SEE ALSOHadron Collider halted for months 20 Sep 08 |

Scientist's promise on collider 10 Sep 08 |

Large Hadron Collider: Guide introduction 03 Sep 08 |

Earth 'not at risk' from collider 23 Jun 08 |

Cern lab goes 'colder than space' 18 Jul 08 |

Failure during Cern magnet test 03 Apr 07 |

RELATED BBC LINKSBBC - Lyn Evans Profile



FROM OTHER NEWS SITES

(kind of)

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Large Hadron Collider will not turnworld to goo, promise scientists

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Times Archive,1974: Black holesmay be explosiveThe young Cambridgeastronomer SteveHawking has suggestedthat these cosmic objectsmay occasionally destroythemselves in violentexplosions

The holes that riddle theuniverse

Hole in spacediscovered

The 'end of the world is nigh' suspicions have been sopowerful that the scientists behind the LHC have publisheda report to allay their fears

Joanna Sugden

Cancel your plans for next Wednesday, it could be yourlast day on Earth. Or could it?

If you believe a vocal lobby of doomsayers, at the flick ofa switch on the Large Hadron Collider (LHC) next weekthe world will be consumed from the inside out andturned to a pile of grey goo. Yesterday their apocalypticwarnings were challenged by a report from the scientistsbehind the project outlining just how safe it is to recreatethe Big Bang under the France-Switzerland border.

The Large Hadron Collider - the atom-smashing machinebuilt underneath the Alps - has sent more internet-basedharbingers of doom into a spin than it will have atomicparticles whizzing around its 17-mile circumference whenit is put into action next week. They fear that the energiesreleased will be so powerful that a runaway black holewill be created that will engulf the planet or produce“quantum strangelets” transforming the Earth into a deadlump of “strange matter”.

So worried are they about the impending end of theUniverse that they have been to court to try to stop it.

Walter L. Wagner and LuisSancho in Hawaii sought atemporary restraining order onscientists at the EuropeanOrganisation for NuclearResearch, or CERN, who theysay have played down thechances that the collider couldproduce a tiny black hole,which could eat the Earth.They say that CERN hasfailed to provide anenvironmental impactstatement as required underthe National EnvironmentalPolicy Act.

Their objections have been sovehement that the scientistsbehind the LHC have

Andrew Halden

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Large Hadron Collider: Scientists'wish list for the LHCFrom the particle that gives everything its mass, to miniblack holes and extra spatial dimensions, the LHC has thepotential to make a host of amazing discoveries

Ian Sample, science correspondentguardian.co.uk, Wednesday 10 September 2008 13.37 BST

larger | smaller

Simulation of a detection of the Higgs boson. Photograph: Cern

When the Large Hadron Collider is up to full power, it will be crashing protons

together 600 million times per second. After each impact, giant detectors will

scour the subatomic wreckage looking for evidence of new physics.

Scientists have some pretty good hunches about what the machine might find,

from creating never-seen-before particles to discovering hidden dimensions

and dark matter, the mysterious substance that makes up 25% of the universe.

Supersymmetry

Many physicists believe that deep down, all the forces of nature are linked,

including gravity, electromagnetism, the strong force – which binds the

constituents of atomic nuclei together – and the weak force – which governs

radioactive decay in stars.

One of the most compelling theories that achieves this unification is called

supersymmetry, which predicts that every fundamental particle in the

universe has an invisible, overweight twin. The theory has spawned a plethora

of bizarre names, such as the squark, the twin of the quark, and the photino,

Could 2009 be a scary year for particle physics?

2

22/10/2009 12:47BBC NEWS | Science & Environment | LHC gets colder than deep space

Page 1 of 3http://news.bbc.co.uk/1/hi/sci/tech/8309875.stm

BBC NEWS CHANNEL

It's a bit like firing knittingneedles from across the Atlanticand getting them to collide halfway

James Gillies, director ofcommunications, Cern

BBC Radio 4 Material World: Oneyear on from the LHC's switch-on


The giant Atlas detector will search for hints of the elusive Higgs boson particle

The Large Hadron Collider (LHC) experiment has once againbecome one of the coldest places in the Universe.

All eight sectors of the LHC have now been cooled to their operatingtemperature of 1.9 kelvin (-271C; -456F) - colder than deep space.

The large magnets that bend particle beams around the LHC arekept at this frigid temperature using liquid helium.

The magnets are arranged end-to-end in a 27km-long circular tunnelstraddling the Franco-Swiss border.

The cool-down is an important milestone ahead of the collider'sscheduled re-start in the latter half of November.

The LHC has been shut downsince 19 September 2008, when amagnet problem called a "quench"caused a tonne of liquid helium toleak into the LHC tunnel.

After the accident, the particleaccelerator had to be warmed upso that repairs could take place.

The most powerful physics experiment ever built, the Large HadronCollider will recreate the conditions just after the Big Bang. It isoperated by the European Organization for Nuclear Research (Cern),based in Geneva.

Two beams of protons will be fired down pipes running through themagnets. These beams will travel in opposite directions around themain "ring" at close to the speed of light.

At allotted points around the tunnel, the proton beams cross paths,smashing into one another with cataclysmic energy. Scientists hopeto see new particles in the debris of these collisions, revealingfundamental new insights into the nature of the cosmos.

Awesome energy

The operating temperature of the LHC is just a shade above"absolute zero" (-273.15C) - the coldest temperature possible. Bycomparison, the temperature in remote regions of outer space is













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Page last updated at 13:46 GMT, Friday, 16 October 2009 14:46 UK


LHC gets colder than deep space

SEE ALSOScientist on French terror charge 12 Oct 09 | Europe

LHC gets warning system upgrade 28 Sep 09 | Science & Environment

Collider 'needs warning system' 05 Dec 08 | Science & Environment

Hadron Collider repairs cost £14m 17 Nov 08 | Science & Environment

Collider halted until next year 23 Sep 08 | Science & Environment

What happened to the Big Bang machine? 20 Sep 08 | Science & Environment

Hadron Collider halted for months 20 Sep 08 | Science & Environment


RELATED INTERNET LINKSLarge Hadron Collider (LHC)






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22/10/2009 14:42BBC NEWS | Science & Environment | LHC gets warning system upgrade

Page 1 of 3http://news.bbc.co.uk/1/hi/8270427.stm

BBC NEWS CHANNEL

It will allow us toconstantly monitor the status ofthe interconnections

Gianluigi Arduini, Cern

BBC Radio 4 Material World: Oneyear on from the LHC's switch-on


Cern has spent about 40m Swiss Francs (£24m) on repairs to the LHC

Engineers hope an early warning system being installed at theLarge Hadron Collider could prevent incidents of the kindwhich shut the machine last year.

The helium leak last September, which resulted from a "faulty splice"between magnets, has delayed the start of science operations bymore than a year.

Officials aim to re-start the collider, known as the LHC, in mid-November.

The vast physics lab is built inside a 27km-long circular tunnelstraddling the French-Swiss border near Geneva.

The LHC will send two beams of particles crashing into each other atclose to the speed of light. Scientists hope to see new particles inthe debris of these collisions, revealing fundamental new insights intothe nature of the cosmos and how it came into being.

This LHC "ring" is split into eightdistinct parts, or sectors. Six ofthese are now at or close to theiroperating temperature of 1.9kelvin (-271C; -456F).

Engineers are powering upmagnets in three sectors toprepare for the injection of proton beams into the ring.

A low-intensity beam could be injected into the LHC in the secondhalf of October, officials told the BBC.

This beam test would involve only parts of the collider, rather thanthe whole "ring". If all goes to plan, the first beam collisions couldoccur before the end of the year.

Machine repairs

The collider has been shut down since 19 September 2008, when amagnet problem called a "quench" caused a tonne of liquid helium toleak into the LHC tunnel.

An investigation carried out for the European Organization forNuclear Research (Cern), confirmed the cause of the accident wasan electrical fault in one of the splices, or "interconnects", linking


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Page last updated at 08:25 GMT, Monday, 28 September 2009 09:25 UK


LHC gets warning system upgrade

SEE ALSOCollider 'needs warning system' 05 Dec 08 | Science & Environment

Hadron Collider repairs cost £14m 17 Nov 08 | Science & Environment

Collider halted until next year 23 Sep 08 | Science & Environment

What happened to the Big Bang machine? 20 Sep 08 | Science & Environment

Hadron Collider halted for months 20 Sep 08 | Science & Environment


RELATED INTERNET LINKSLarge Hadron Collider (LHC)






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2009 should be the really exciting year!

The cross-section of the ion beam flowing through the LHC, just before the ALICE detectorPhoto: CERN

Games Offers

The Large Hadron Collider at Cern is fired up forfirst time since 'quench'The Large Hadron Collider at Cern in Geneva has been fired up for the first timesince its high-profile failure last year.

By Tom ChiversPublished: 12:32PM GMT 27 Oct 2009

The huge particleacceleratorsuccessfullypowered someprotons and leadions around shortsections of its 17-mile ring onFriday, andeverything seemedto be workingcorrectly.

Engineers andscientists

(http://http://www.telegraph.co.uk/science/) have been warily putting it through its paces for the first timesince its catastrophic breakdown, or “quench”, which happened when two of the LHC(http://www.telegraph.co.uk/science/large-hadron-collider/) ’s huge superconducting magnets suffered a shortcircuit within days of it powering up (/science/large-hadron-collider/3352108/Large-Hadron-Collider-broke-down-

hours-after-launch.html) .

29/10/2009 01:01The Large Hadron Collider at Cern is fired up for first time since 'quench' - Telegraph

Page 1 of 4http://www.telegraph.co.uk/science/large-hadron-collider/6445829/Th…adron-Collider-at-Cern-is-fired-up-for-first-time-since-quench.html

The cross-section of the ion beam flowing through the LHC, just before the ALICE detectorPhoto: CERN

Website of the Telegraph Media Group with breaking news, sport, business, latest UK and world news. Content from the Daily Telegraph and Sunday Telegraph newspapers and video from Telegraph TV.

JobsDatingGames Offers

The Large Hadron Collider at Cern is fired up forfirst time since 'quench'The Large Hadron Collider at Cern in Geneva has been fired up for the first timesince its high-profile failure last year.

By Tom ChiversPublished: 12:32PM GMT 27 Oct 2009

The huge particleacceleratorsuccessfullypowered someprotons and leadions around shortsections of its 17-mile ring onFriday, andeverything seemedto be workingcorrectly.

Engineers andscientists

(http://http://www.telegraph.co.uk/science/) have been warily putting it through its paces for the first timesince its catastrophic breakdown, or “quench”, which happened when two of the LHC(http://www.telegraph.co.uk/science/large-hadron-collider/) ’s huge superconducting magnets suffered a shortcircuit within days of it powering up (/science/large-hadron-collider/3352108/Large-Hadron-Collider-broke-down-

hours-after-launch.html) .

3

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The ATLAS detector (toroidalmagnet system)

News & EventsHome News & Events Edinburgh joins the ATLAS collaboration

Edinburgh joins the ATLAS collaborationPublished on Tue, 20 Oct, 2009 at 15:36

Physicists from Edinburgh are to join the questfor the Higgs boson particle at CERN inSwitzerland.

The researchers will join the international ATLAScollaboration seeking to verify the existence ofthe theoretical sub-atomic particle, a crucial partof the Standard Model of Particle Physics andCosmology.

The ATLAS experiment aims to address the mostimportant unsolved questions in the universe, i.e., whether or not, the Higgsboson exists, and what the fundamental particle mass generation mechanism is.It could also discover the origin of dark matter and new physics models of nature(e.g. super-symmetry).

Higgs theoryEmeritus Professor Peter Higgs predicted the existence of the Higgs particlewhile working at the University in the 1960s. If experiments at CERN’s massiveatom-smasher prove the Professor’s theory correct, he is tipped to win theNobel Prize for physics.

Joining the research at CERN are Dr Philip Clark, Dr Victoria Martin, Dr AndyBuckley, Dr Wahid Bhimji and Dr Andy Washbrook together with students BenWynne, Ben Smart and Brendan O’Brien and technician Andrew Main.

They will work on the ATLAS detector, one of four experiments analysisingcollisions at the Large Hadron Collider as it aims to recreate the conditions ofthe Big Bang.

Impact of researchTheir work will involve modelling and simulating the particle collision process inorder to understand the detector response and the complex data produced bythe experiments. They will also contribute to the operation of the detector itselfand provide software to manage the data produced.

Global partnershipPhysicists from Edinburgh are already involved in another project at CERN(LHCb) but, until now, have not taken part directly in the search for the HiggsBoson.

The Edinburgh team joins the collaboration, involving 2900 people in 37countries, after a year of preparatory work with support from colleagues in theScottish Universities Physics Alliance.

Hot off the press: Edinburgh joins the LHC effort!

4

Subatomic Physics:

Particle Physics Lectures“Physics of the Large Hadron Collider”

5

Particle Physics Lectures OutlineLecture 1 - Introduction

The Standard Model of particle physics

The fundamental particles and forces

Lecture 2 - Practical Particle Physics

Measuring particle physics

Units, decays, scattering

Quantum numbers

Lecture 3 - Quantum Electrodynamics (QED)

Anti-particles

Quantum description of electromagnetism

Feynman diagrams

Lecture 4 - The LHC

Particle acceleration

Colliders

Lecture 5 - The ATLAS Detector

Interactions of particles in matter

Collider Detectors

Lecture 6 - Particle Physics at Past Colliders

The Large Electron Positron Collider

Evidence for quarks and colour

e+e!→ hadrons

Lecture 7 - Protons, Quarks and Strong Interactions

Gluons, hadronisation

Quark Confinement

Running coupling constant

Lecture 8 - Weak Interactions

Muon and tau decay

Weak quark decays

Lecture 9 - Electroweak and the Higgs boson

W and Z bosons

The Higgs mechanism

Lecture 10 - Beyond the Standard Model

Supersymmetry

Extra dimensions ...

6

Particle Physics and Me

My research deals with Particle Physics at Colliders.

I’m currently involved with three projects:

CDF

p p1.96 TeV

2.The ATLAS experiment at the Large Hadron Collider. The LHC collides protons on protons at 14 TeV.

3.The international linear collider (ILC). Design is to collide electrons and positrons at 0.5 - 1 TeV (or more?)

1. The CDF experiment at the Fermilab Tevatron, near Chicago. The Tevatron collides protons and anti-protons at ~2TeV.

Dr Victoria MartinJCMB room 5419 [email protected]

7

Most up to date:

• Level of this course: Particle Physics, by B.R. Martin & G. Shaw, 3rd edition (Wiley 2008)

- 10 copies in JCM Library

• More advanced: Introduction to Elementary Particles by D. Griffiths, 2nd edition (Wiley 2008)

- 4 copies in JCM Library

Oldies (but goodies):

• Introduction to High Energy Physics - D.H. Perkins, 4th edition (CUP 2000)

• Quarks and Leptons –F. Halzen & A.D. Martin (Wiley 1984)

Further Resources:

• For more information that you could ever need on every particle ever: http://durpdg.dur.ac.uk/lbl/

• Information about LHC and LHC physics: www.cern.ch www.atlas.ch

Books etc• In conjunction with attending the lectures you will need to read around the

subject to fully understand the material.

8

Subatomic Physics:

Particle Physics Lecture 1Our current understanding:

“The Standard Model of Particle Physics”

9

atom

nucleus

protons &neutrons

quarks &electrons

From the Atom to Subatomic

}Nuclear Physics

}Particle Physics

from introductory Subatomic slides

10

} Particle Physics

Subatomic physics looks at:

•(very) short distances

•(very) early time in the universe

•(very) high energy densities

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History of the Universe

} Nuclear Physics


11

The Standard ModelThe current understanding of the fundamental particles and the interactions between them is called the “Standard Model of Particle Physics”. Boson-mediated

FORCESBoson-mediated

FORCES

Gravity ?

Electro-magnetism photon

Weak

Strong

W±

Z0

!

gluons12

Basic Particles (1st Generation)

•Nuclear physics description of beta decay: n ! p e! "#e

•Particle physics description of beta decay: d ! u e! "#e

Particle SymbolElectric Charge

Type

electron e" -1 lepton

neutrino #e 0 lepton

up-quark u +2/3 quark

down-quark d !1/3 quark

Basic Constituents of MatterFour spin-"ℏ fermions

The particles that you know already, e.g. from beta decay: n ! p e! "#e

LeptonsElectron and neutrino

QuarksNucleons are bounds states of up-quarks and down-quarks

• In addition to electric charge, every quarks carries an additional “colour charge” quantum number: either red, blue or green.

13

Higher GenerationsNature replicates itself: there are three generations of quarks and leptons

1st Generation1st Generation 2nd Generation2nd Generation 3rd Generation3rd Generation charge,e

electron e" muon $" tau %" -1

electron neutrino #e muon

neutrino #$ tau neutrino #% 0

down quark d strange quark s bottom

quark b !⅓up quark u charm quark c top quark t +⅔

Ordinary Matter: built from the 1st generation

Higher Generations:• copies of (#e, e", u, d)• undergo identical interactions• only difference is mass of particles• generations are successively heavier

Why 3 generations?symmetry/structure not understood!

14

Antiparticles

Compared to its matter partner, an antiparticle has:

•equal mass

•opposite electric charge

•opposite “additive” quantum numbers

Example: positron (e+) antiparticle of the electron (“anti-electron”)Discovered in 1931 by Carl Anderson

Notation: bar over symbol or minus ↔ plus

e.g. for first generation:

Combining relativity and quantum mechanics implies every particle has a corresponding antiparticleAntiparticles of the SM particles are antimatter

“Track” left by a positron

u↔ u d↔ d e− ↔ e+ νe ↔ νe

More in PP Lec 2 (& Quantum Physics §14.5)

15

Subatomic Forces

•At subatomic scales interactions between particles and nuclei are caused by the three subatomic forces:

•The electromagnetic force

•The weak nuclear force

•The strong nuclear force

•The interactions due to these forces are evident in:

•Scattering: e.g. scattering of protons on protons at the LHC

•Particle Decay: e.g. decay of radioactive nuclei, decays of cosmic-ray muons

•Nuclear Fission and Fusion, e.g.: reactions in a nuclear reactor

23592 U + n→ 236

92 U→ 14456 Ba +89

36 Kr + 3n


16

The Forces of Particle Physics

•Quantum mechanical description uses “messenger particles” to propagate the force between particles.

•Messenger particles are spin-1ℏ bosons

•e.g. beta decay n!p e! "#e propagated by a W! boson

Strong • Strongest force• Acts on quarks only

Electromagnetic• 2nd strongest force• Acts on charged particles

Weak• 3rd strongest force• Acts on all particles

Gravity• weakest force - negligible at PP

scale• Acts on all particles

time

• propagated by (8) gluons, g • propagated by photon, $

• propagated by W± and Z0 bosons

17

What do the particles do?

Particles interact via one of the forces: strong, electromagnetic or weak.

Two main interactions:

•Particle scattering

•can be elastic or inelastic

•we’ll mainly consider inelastic scattering

•e.g. scattering of electron and positron, producing a pair of muons e+e!%µ+µ!

•Particle decay

•e.g. Beta decay: d ! u e! "#e•e.g. Muon decay: µ!%e! "#e "µ

23

Higher Orders

So far only considered lowest order term in the

perturbation series. Higher order terms also

contribute

Lowest Order:

e-

e+

µ-

µ+!

Second Order:

e-

e+

µ-

µ+

e-

e+

µ-

µ+

+....

Third Order:

+....

Second order suppressed by relative to first

order. Provided is small, i.e. perturbation issmall, lowest order dominates.

Dr M.A. Thomson Lent 2004

6

Summary of Standard Model Vertices

! At this point have discussed all fundamental fermions

and their interactions with the force carrying bosons.

! Interactions characterized by SM vertices

ELECTROMAGNETIC (QED)

!

e-

e-

e

" =e

2

4# !

q

q

Q e

Couples to CHARGE

Does NOT change

FLAVOUR

STRONG (QCD)

"s =

gs2

4# g

q

q

gs

Couples to COLOUR

Does NOT change

FLAVOUR

WEAK Charged Current

W-

e-

$e

gw

"w

=g

w2

4# W+

u

d’g

wV

ckm

Changes FLAVOUR

For QUARKS: coupling

BETWEEN generations

WEAK Neutral Current

Z0

e-, $

e

e-, $

e

Z0

q

q

Does NOT change

FLAVOUR


µ!

e!

"µ

"#eW

6

Summary of Standard Model Vertices

! At this point have discussed all fundamental fermions

and their interactions with the force carrying bosons.

! Interactions characterized by SM vertices

ELECTROMAGNETIC (QED)

!

e-

e-

e

" =e

2

4# !

q

q

Q e

Couples to CHARGE

Does NOT change

FLAVOUR

STRONG (QCD)

"s =

gs2

4# g

q

q

gs

Couples to COLOUR

Does NOT change

FLAVOUR

WEAK Charged Current

W-

e-

$e

gw

"w

=g

w2

4# W+

u

d’g

wV

ckm

Changes FLAVOUR

For QUARKS: coupling

BETWEEN generations

WEAK Neutral Current

Z0

e-, $

e

e-, $

e

Z0

q

q

Does NOT change

FLAVOUR


d

e!

u

"#eW

timesee: JH D&R lectures 2, 14, 15

We’ll learn all about

these type of diagrams

throughout the course

18

Mesons = qq Bound states of quark anti-quark pairBosons: spin 0, 1ℏ, 2ℏe.g. pions

Baryons = qqqThree quark bound statesFermions: spin 1/2ℏ, 3/2ℏ ...e.g. proton (uud), neutron (udd) anti-baryons e.g. anti-proton

•

• Free quarks have never been observed - quarks are locked inside hadrons

• Hadrons are bound states of quarks: either (qqq) or (qq ) • Charge of hadron is always integer multiple of electric charge, e

• Colour charge of hadron is always neutral

• Two types of hadrons – mesons and baryons (also anti-baryons! q q q)

Hadrons: Mesons & Baryons

qq

qq

q

p = (uud)n = (udd)p = (uud)

π+ = (ud)π− = (ud)

π0 =1√2(uu− dd)

19

• 3 generations of quarks & leptons

• Antimatter partner for each fermion

• Quarks bind together to form hadrons - mesons and baryons

Summary

An elegant theory that describes accurately (almost) all measurements in particle physics

The Standard Model of Particle Physics

Quarks and LeptonsQuarks and LeptonsQuarks and Leptons Charge, e

"ee

"µµ

"&&

0!1

ud

cs

tb

+2/3!1/3

Interaction Gauge Bosons

Charge, e

Strong gluons, g 0

Electro-magnetic Photon, $ 0

Weak W, Z 0, ±1

Gravity graviton? 0

Matter Forces

•mediated by the exchange of spin-1ℏ bosons

• fermions, spin-"ℏ

20

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